Accumulated evidence shows that gut microbial composition is closely related to the development of colorectal cancer.Germ-free animal models,especially germ-free murine models,have been shown to be simple and easy to access,which provide a valuable tool for studying the correlation between microbiota,colorectal neoplasms and the host.These models are mainly established by cesarean section followed by rearing and breeding the pups in sterile isolators.Similarly,some special models,such as transgenic and drug-induced murine models,can also be developed according to the study purposes.To date the germ-free murine models have been widely used in the field of colorectal cancer research,showing that certain microbes or microorganisms can promote the occurrence and development of colorectal cancer by activating immune response and inducing inflammation.Results from germ-free murine models have demonstrated that gut microbial dysbiosis and colorectal cancer development influence each other and are reciprocal causation.Taken together,germ-free murine models are important tools for investigating the mechanisms of the tumorigenesis in colon and rectum,especially dysbiosis-induced colorectal cancer.